Area Forecast Discussion
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FXUS62 KRAH 231843
Area Forecast Discussion
National Weather Service Raleigh NC
240 PM EDT Thu Mar 23 2017
Continental polar high pressure will continue to modify over the srn
Middle Atlantic states through tonight. A warm front will retreat
north across the region on Fri, as the high drifts east toward
.NEAR TERM /THROUGH TONIGHT/...
As of 1110 AM Thursday...
Little adjustment required to the near term forecast.
An area of high pressure at the surface and aloft will maintain
relatively cool and dry conditions across central NC through tonight.
After a chilly start to the day, with early morning temperatures in
the upper 20s-lower 30s, temperatures this afternoon should recover
into the low-mid 50s north and upper 50s south. Aside from a few
passing thin cirrus, skies will remain sunny. ~WSS
The surface ridge will continue to extend across NC tonight.
Associated calm to light ESEly surface winds, combined with a mainly
clear sky, aside from continued occasional thin cirrus, will favor
strong radiational cooling and a light freeze away from urban
centers. Low temperatures in the upper 20s to middle 30s. ~MWS
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 355 AM Thursday...
Surface high pressure will drift to near and just north of Bermuda;
and associated return flow across the sern U.S. will allow a warm
front to retreat north through central NC during the day Fri. Both
temperatures and moisture will consequently be on the increase, with
highs in the mid-upper 60s N and NW, to lower 70s in the S, and
surface dewpoints in the 40s to near 50 degrees. The increasing low
level moisture values, and broad WAA regime, will favor a scattering
of flat/fair weather cumulus trapped beneath a subsidence inversion
that will have become established courtesy of mid-upper level ridging
Not as cool Fri night, though with decent radiational cooling
potential as the Bermuda surface ridge continues to extend west into
NC. Patchy radiation fog may result, with low temperatures in the
middle 40s to around 50 degrees.
.LONG TERM /Saturday through Thursday/...
-- Changed Discussion --As of 240 PM Thursday...
High confidence in warm weather through the early part of next week,
with bouts of showery weather, primarily on Sunday and Tuesday.
Uncertainty grows midweek and beyond as differences emerge regarding
their handling of polar low deepening over SE Canada and the
adjacent NW Atlantic waters, however it appears certain that the
wavy active southern stream pattern will persist through next week.
Sat/Sat night: The potent mid level low will cross the central Miss
Valley as its southward-extending trough takes on a negative tilt
over the Mid South and Gulf States, leading to strengthening mid
level flow from the SW into the Carolinas. PW will remain elevated,
in the 75th percentile, with a light onshore-directed southeasterly
flow drawing in increasing low level moisture. We should see
considerable morning stratus and fog, particularly over the western
half of the CWA where low level moist upglide will be deepest, and
these clouds should lift to scattered to broken stratocumulus (more
clouds west than east) with heating, and these should persist
through the day, topped with high thin clouds. Very dry/stable mid
levels will keep the day mostly dry, apart from possible patchy
morning drizzle in the western Piedmont. Thicknesses will continue
to trend above normal, supporting highs of 70-76 NW to SE. The mid
level low tracks slowly from MO to IL Sat night, bringing the
negatively tilted trough axis and its DPVA into the western
Carolinas. This southerly steering flow will drive up PW to nearly
200% of normal just to our west and into the far NW Piedmont late
Sat night, in tandem with the arrival of 25-35 kt low level jetting
into the Srn Appalachians. Will bring in good chance pops very late
Sat night into the far W CWA. Lows Sat night mainly in the mid 50s.
Sun/Sun night: The mid level low will quickly weaken and fill as it
approaches Lower MI Sun, while the trailing trough axis pivots
northeastward through our area. The best precip chances (likely to
categorical) will track ENE through central NC (especially NW) Sun
morning into early afternoon beneath a band of enhanced upper
divergence, with PW rising further to 250% of normal as steering
flow becomes southwesterly. Despite the moist column, the dwindling
dynamic forcing for ascent as this system tracks NE through the Mid
Atlantic region will lead to a tapering down of precip chances
through Sun, especially over our SE sections, as the core of the
peak integrated water vapor transport shifts to our NNE. Only low
chances are expected Sun night as the dampening mid level trough
axis shifts to our NE with gently rising heights aloft, within a
continued very moist column. Expect highs of 70-78 followed by lows
in the upper 50s with overnight stratus developing.
Mon-Tue: Monday will feature just patchy light precip at most over
much of central NC as a mid level ridge axis shifts overhead with a
weak cap at 925 mb and dry mid-upper levels, although higher PW
settling over eastern NC and higher surface dewpoints may prompt
greater convection coverage over our SE. Our next mid level trough
in this active pattern will push through the eastern third of the
CONUS Mon night through Tue, accompanied by a surface cold front.
Important model differences start to emerge, with the GFS slower and
more amplified than the weaker/faster ECMWF. Will lean toward the
more progressive ECMWF given this active pattern, but confidence is
not high. Will maintain good chance of showers and storms Mon night
through Tue. Highs 75-80 Mon/Tue with thickness over 35 m above
normal. Lows in the upper 50s.
Wed-Thu: Model details differ, but in general, heights will rise
over the Southeast in the wake of the departing trough, as another
powerful and deep low tracks over the Southwest states. Expect dry
weather and cooler temps, still near or just above seasonal normals,
as surface high pressure builds in from the north. -GIH
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.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 125 PM Thursday...
High probability that VFR conditions will occur across central NC
through 00Z Saturday. The exception will be the potential for a few
patches of MVFR visibility due to fog in sections of the southern
Piedmont, the Sandhills, and the southern coastal plain, between 10Z-
The area of high pressure which has provided the VFR conditions will
drift offshore Friday. The return sly flow will begin to advect a
warm moist air mass into central NC. The arrival of this air mass
will lead to higher chances for early morning fog or low stratus
Saturday morning and Sunday morning.
An approaching low pressure system will increase the threat for
scattered showers Sunday through Tuesday. With the moist air mass in
place, there will be periods of IFR/MVFR ceilings during this same